No, You Don't Do CrossFit
That title should have caught some eyes! Let us explain.
CrossFit is a total prescription. Not just x rounds for time or pairing weightlifting with gymnastics. While CrossFit does offer us some kick-ass workouts, the truth is, unless you're following the full prescription you'll never see the full results.
So what is the full prescription? Let's go back to October 2002 and read "What Is Fitness?" which was published by Coach Glassman.
TL;DR? Luckily for you Coach is a fan of elegance and describes world class fitness in 100 words here:
Eat meat and vegetables, nuts and seeds, some fruit, little starch and no sugar. Keep intake to levels that will support exercise but not body fat.
Practice and train major lifts: Deadlift, clean, squat, presses, C&J, and snatch. Similarly, master the basics of gymnastics: pull-ups, dips, rope climb, push-ups, sit-ups, presses to handstand, pirouettes, flips, splits, and holds. Bike, run, swim, row, etc, hard and fast.
Five or six days per week mix these elements in as many combinations and patterns as creativity will allow. Routine is the enemy. Keep workouts short and intense.
Regularly learn and play new sports.
You'll notice the first paragraph entirely references nutrition. Look, long story short because we're into that sort of thing:
You cannot eat whatever the hell you want and claim to be 'doing CrossFit' - sorry. Your diet doesn't have to be perfect, and you don't have to be 100% compliant 100% of the time. *Note: That's not to say go crazy! However, if your goal is weight loss don't blame CrossFit if you don't see progress. Especially if you're only following the pieces of advice that you like.